Endless accumulating under/over conveyors with upper and lower runs adapted to slidably support pallets and to frictionally transport them over the upper and lower runs have been previously developed. One such conveyor with a drive mechanism for positively advancing pallets from one run to the other over a curved section at each end of the conveyor is disclosed in U.S. Pat. No. 4,934,515.
As a practical matter, in this type of conveyor, the maximum length of the pallet in its direction of travel along the run is limited by the need to advance each pallet over the curved sections at the end of the conveyor. The maximum length of a pallet often limits the maximum length or size of a workpiece that can be carried by the pallet. To permit carrying longer workpieces, U.S. Pat. No. 5,407,058 and EPO Patent 0 462 878A1 disclose a conveyor with pallet trains of two more succeeding pallets permanently connected together by links pivoted at each end to an adjacent pallet.